Sorry. As a California part-year resident, California will tax all world-wide income that is paid to you while you are living in CA, regardless of where you were living when it was earned. The bonus will also be taxable in Massachusetts to the extent it relates to work you performed while living in MA. In other words, if you continue to work for the same overall employer, and you lived for 75% of 2023 in MA, then 75% of your wages (including the bonus) are taxable in MA, even if they were paid while you were living in CA. If you are changing employers, and 100% of your bonus will be a result of work performed while you were living in MA, then 100% of the bonus will be taxable in MA, and also in CA.
You should expect to prepare a part-year resident CA return and a part-year resident MA return. CA should give you a credit toward income that is taxed in both states, but you may want to use a professional this year to make sure the income and credits are reported correctly.
